$plants->[$i]{'common'} =  $plants->[$i]{'common_name'};
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And few lines later, you try to store something in a hash ref:

    $plants->[$i]{'common'}->[$jctr]{'sizes'} = $sizes->[$j]{'plantsiz
+e'}.$sizes->[$j]{'unit'};
#   ~~~~~~~~~~~~~~~~~~~~~~~
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The underlined thing is a string (comment mine). You can't use a string as a hash ref under strict.

BTW, is $jctr ever different to $j (and $kctr to $k )? If not, you can improve readability by dropping two variables.

($q=q:Sq=~/;[c](.)(.)/;chr(-||-|5+lengthSq)`"S|oS2"`map{chr |+ord
}map{substrSq`S_+|`|}3E|-|`7**2-3:)=~y+S|`+$1,++print+eval$q,q,a,
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